The Fåhraeus-Lindqvist effect is a blood flow phenomenon based on erythrocyte fluidity and related to blood viscosity. Viscosity is lower in vessels of the circulatory periphery with a narrow lumen than in vessels with a higher lumen. The Fåhraeus-Lindqvist effect primarily prevents blood stasis in capillaries.
What is the Fåhraeus-Lindqvist effect?
The Fåhraeus-Lindqvist effect is a phenomenon of blood flow based on the fluidity of erythrocytes and related to the viscosity of blood. Human blood has a certain viscosity. Viscosity corresponds to a measure of the viscosity of body fluids. The thinner a fluid is, the lower its viscosity. An alternative is to measure viscosity by means of strain. The term Fåhraeus-Lindqvist effect is used to describe a decrease in blood viscosity that is accompanied by a decreasing diameter of the vessels and thus a decreasing elongation. The vessel diameter drops below 300 µm, preventing blood stasis in the capillaries. The Fåhraeus-Lindqvist effect is based on the natural properties and capabilities of erythrocytes. The phenomenon is considered to be the reason why the viscosity of blood in vessels of the circulatory periphery is considerably lower than in vessels of the central circulation with a higher lumen because of the narrow lumen. The deformability of blood cells associated with the effect is also called fluidity and is considered a prerequisite for the Fåhraeus-Lindquist effect phenomenon.
Function and task
Red blood cells are also called erythrocytes and have a certain fluidity. Thus, they can deform. The deformation is due to the shear forces experienced by the blood cells near the walls of the blood vessels. The resulting shear forces displace the erythrocytes. Thus, the red blood cells migrate into the axial flow. This phenomenon is also known as axial migration and gives rise to cell-poor marginal currents. The cells are surrounded by an edge current of plasma. In the Fåhraeus-Lindquist effect, this edge current takes on the role of a sliding layer. Apparently, the blood flows more fluidly in these areas. This connection is related to the influence of hematocrit on the level of peripheral resistance. The hematocrit corresponds to the volume fraction of cellular blood elements. Red blood cells make up 96 percent of it and correspond to the largest fraction. Peripheral resistance corresponds to the resistance to flow in the body’s bloodstream and is the sum of all peripheral vascular resistances. The Fåhraeus-Lindqvist effect lowers the hematocrit influence on peripheral resistance in smaller blood vessels below 300 µm. The phenomenon also reduces frictional resistance in these vessels. In larger blood vessels, on the other hand, there is a high friction of the flowing cells. The low-cell marginal flow does not widen effectively in larger cells. This relationship causes the viscosity of the blood to increase. This viscosity also increases in extremely narrow capillary vessels. Although erythrocytes have fluidity, they cannot deform further beyond a certain point. In summary, the apparent blood viscosity in vessels of up to ten micrometers is only slightly higher than in plasma due to the Fåhraeus-Lindqvist effect. The decrease in viscosity is due to the erythrocytes, which move all the faster in the center of the blood stream because of the smaller shear forces. For this reason, they increasingly move near the center, which is called axial migration. In this way, a cell-poor sliding layer is formed in the peripheral zone and the locomotion of the fluid in the center is accelerated. Because of their fluidity, erythrocytes can adapt to altered shear stresses and reduce any perturbation effects on hemodynamics.
Diseases and disorders
Complaints associated with the Fåhraeus-Lindqvist effect can have a wide variety of causes. In most cases, disturbances in general hemodynamics are responsible for complaints of this type. Such disturbances may, for example, be related to pathological changes in the blood vessels. Pathologically altered blood vessels may in turn be due to diseases such as arteriosclerosis. This slowly progressive disease often remains asymptomatic for many years and in many cases is not diagnosed until late.In arteriosclerosis, blood fats, thrombi or connective tissue are deposited in the blood vessels, causing plaques to form and narrowing the vessel lumen. Such restricted blood flow promotes secondary diseases. In addition to or together with diseases such as arteriosclerosis, high vascular stresses and cracks that develop in this way can also cause disturbances in blood flow and the Fåhraeus-Lindqvist effect. Bleeding through cracks, for example, promotes the formation of thrombi. The blood vessels lose their elasticity, become rigid and visibly harden. The Fåhraeus-Lindqvist effect can also be impaired if the composition of the blood changes. This is the case, for example, when there is a lack of fluids. The same applies when certain medications are taken, such as ovulation inhibitors. Increased clotting factors after surgery or major burns also change the blood composition. Another conceivable connection for altered compositions is platelet aggregation. Thrombosis is often favored by the aforementioned phenomena. In addition to obesity and advanced age, risk factors for thrombosis include regular nicotine or alcohol abuse, general hypertension, and diabetes mellitus. In addition, congenital abnormalities of the red blood cells can disrupt blood flow and with it the Fåhraeus-Lindqvist effect. Genetic alterations related to red blood cells are manifested, for example, in sickle cell anemia, which is associated with a sickle-shaped appearance of red blood cells. In addition, metabolic diseases and iron or vitamin deficiencies have negative effects on red cell balance. Because the Fåhraeus-Lindqvist effect prevents blood stasis in the capillaries, disturbances of the effect may lead to capillary blood stasis and are often initially noticeable as skin redness or protruding veins.
